There has been proposed a film forming apparatus, e.g., a CVD (chemical vapor deposition) apparatus, for performing a film formation by using a source gas generated by vaporizing a liquid source material of an organic metal or a liquefied source material of an organic metal dissolved in a solvent. A typical example of such a film forming apparatus is an MO (metal organic) CVD apparatus, which is employed in forming a high-k dielectric thin film of, e.g., a PZT (Pb—Zr—Ti oxide), a BST (Ba—Sr—Ti oxide), and the like; a metal thin film of, e.g., tungsten (W); a semiconductor thin film of, e.g., InP (see, e.g., JP10-177971A); and so forth. The CVD can be classified into a thermal CVD, an optical CVD, a plasma CVD, and so forth depending on the type of energy supplied to trigger a chemical reaction.
In the film forming apparatus described above, fine particles (hereinafter, simply referred to as “particles”) are often generated inside of the vaporizer or in a transport path of a source gas leading to a film forming vessel as a result of solidification or decomposition of source material. The particles thus generated may be introduced into a film forming chamber to be deposited on a substrate, resulting in degradation of a film quality and product failure such as deterioration of an insulation property.
To prevent the problems, there have been proposed a configuration in which a filter is disposed at an outlet of the vaporizer (see, e.g., JP7-94426A); a configuration in which a filter (line filter) is disposed between a gas supply source and the film forming chamber (see, e.g., JP5-68826A); and the like. In these configurations, particles flown from the upstream side of the filters are trapped by the filters, so that the particles are prevented from being flown to the downstream side of the filters, and thus the amount of particles introduced into the film forming chamber can be reduced.
However, in the above methods, though the filters trap the particles flown from the upstream sides, the amount of particles reaching the substrate in the film forming chamber cannot be reduced sufficiently. Though the reason for this is not clearly found out, it is conjectured that, for example, fine particles grow at the downstream sides of the filters after passing through meshes of the filters or fine droplets (residual mist) of the source material become particles at the downstream sides of the filters after passing therethrough.
To prevent these problems, it is considered to improve the trapping efficiency of the filters by means of reducing the size of the meshes of the filters, thus allowing the fine particles or the fine droplets of the source material to be trapped by the filters. However, if the sizes of the meshes are reduced, the filters would be clogged shortly, and in such case, a repair and maintenance work of cleaning or replacing the filters need to be performed more frequently so as to maintain a set supply flow rate of the source gas.
Moreover, particles can also be generated inside the film forming chamber as a result of deposits being peeled off inner surfaces of the chamber or vicinities of the susceptor. Such a problem may not be avoided by reducing the amount of the particles introduced into the film forming chamber from a gas supply line by the filters.